The invention relates to droplet ejection devices. Inkjet printers are one type of droplet ejection device. In one type of inkjet printer, ink drops are delivered from a plurality of linear inkjet printhead devices oriented perpendicular to the direction of travel of the substrate being printed. Each printhead device includes a monolithic semiconductor body that has an upper face and a lower face and defines a plurality of fluid paths from a source of ink to respective nozzles arranged in a single, central row along the length of the device. The fluid paths are typically arranged perpendicular to the line of nozzles, extending to both sides of the device from the central line of nozzles and communicating with sources of ink along the two sides of the body. Each fluid path includes an elongated pumping chamber in the upper face that extends from an inlet (from the source of ink along the side) to a nozzle flow path that descends from the upper surface to a nozzle opening in the lower-face. A flat piezoelectric actuator covering each pumping chamber is activated by a voltage pulse to distort the piezoelectric actuator shape and discharge a droplet at the desired time in synchronism with the movement of the substrate past the printhead device.
In these devices it is desirable to discharge inkdrops that have the same velocity and the same volume in order to provide a uniform image with high quality.
Each individual piezoelectric device associated with each chamber is independently addressable and can be activated on demand to generate an image. The frequency of delivering ink droplets thus can vary from 0 Hz up to some value at which the inkdrop velocity or volume varies to an unacceptable level.